Article

Toxic prefibrillar alpha-synuclein amyloid oligomers adopt a distinctive antiparallel beta-sheet structure.

Biochemical Journal (Impact Factor: 4.78). 01/2012;

ABSTRACT Parkinson's disease is an age-related movement disorder characterized by the presence in the mid-brain of amyloid deposits of the 140-aa protein alpha-synuclein (AS). AS fibrillation follows a nucleation polymerization pathway involving diverse transient prefibrillar species varying in size and morphology. Like for other neurodegenerative diseases, cytotoxicity is currently attributed to these prefibrillar species rather than to the insoluble aggregates. Nevertheless, the underlying molecular mechanisms responsible for cytotoxicity remain elusive and structural studies may contribute to the understanding of both amyloid aggregation mechanism and oligomer-induced toxicity. It is already recognized that soluble oligomeric AS species adopt beta-sheet structures that differ from those characterizing the fibrillar structure. In the present work we used ATR-FTIR spectroscopy, a technique especially sensitive to beta-sheet structure, to get deeper insight into the beta-sheet organization within oligomers and fibrils. Careful spectral analysis revealed that AS oligomers adopt an antiparallel beta-sheet structure whereas fibrils, a parallel arrangement. The data are discussed in terms of regions of the protein involved in the early beta-sheet interactions and the implications of such conformational arrangement for the pathogenicity associated to AS oligomers.

Full-text

Available from: Rabia Sarroukh, Jun 09, 2015
0 Followers
 · 
239 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: There is growing evidence that a variety of biochemical processes that underlie the most frequent neurodegenerative diseases may have much in common with those connected with natural aging. It was shown that they involve, among others, lipid peroxidation and/or generation of insoluble in water protein deposits (i.e. alpha-synuclein and/or beta amyloid). Therefore, it is likely that the analysis of changes in both lipid and protein composition may be interesting in the light of any potential pathologies occurring within the dopaminergic system during physiological aging. Thereby, this paper presents a methodology for the analysis of age-related changes in a lipid and protein composition within human subtantia nigra tissue by means of Fourier Transform Infrared Microspectroscopy (FTIRM). Particularly, the changes in the lipid saturation, unsaturation as well as in the protein secondary structure were examined. The studies were carried out on samples from 35 individuals who died without any signs of neurologic dysfunctions. Our results show that the level of lipid saturation increases inside the subtantia nigra tissue with age, though the total content of lipid decreases with age of individuals. Moreover, the statistically significant decrease in the protein content within neuron bodies was observed. Interestingly, it is presented that the content of the anti-parallel beta sheets for neuron bodies decreases from seventh to eighth decades of life and subsequently markedly increases from eighth to ninth decades of life, whilst, as regards extraneuronal spaces, the opposite trends are reported i.e. increase from the seventh to eighth decades, and subsequent decrease in the ninth decade of life. These observations, though preliminary, shed the light on a putative contribution of various pathological lipid- and protein related processes underlying senescence, suggesting a "biochemical link" between the aetiology of the most common neurodegenerative diseases and physiological aging.
    Neurochemistry International 06/2014; DOI:10.1016/j.neuint.2014.06.014 · 2.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Parkinson's disease (PD) is a devastating neurodegenerative disorder characterized by the loss of neurons in the substantia nigra pars compacta and the presence of Lewy bodies in surviving neurons. These intracellular protein inclusions are primarily composed of misfolded α-synuclein (aSyn), which has also been genetically linked to familial and sporadic forms of PD. DJ-1 is a small ubiquitously expressed protein implicated in several pathways associated with PD pathogenesis. Although mutations in the gene encoding DJ-1 lead to familial early-onset PD, the exact mechanisms responsible for its role in PD pathogenesis are still elusive. Previous work has found that DJ-1 - which has protein chaperone-like activity - modulates aSyn aggregation. Here, we investigated possible physical interactions between aSyn and DJ-1 and any consequent functional and pathological relevance. We found that DJ-1 interacts directly with aSyn monomers and oligomers in vitro, and that this also occurs in living cells. Notably, several PD-causing mutations in DJ-1 constrain this interaction. In addition, we found that overexpression of DJ-1 reduces aSyn dimerization, whereas mutant forms of DJ-1 impair this process. Finally, we found that human DJ-1 as well as yeast orthologs of DJ-1 reversed aSyn-dependent cellular toxicity in Saccharomyces cerevisiae. Taken together, these data suggest that direct interactions between DJ-1 and aSyn constitute the basis for a neuroprotective mechanism and that familial mutations in DJ-1 may contribute to PD by disrupting these interactions.
    Cell Death & Disease 07/2014; 5:e1350. DOI:10.1038/cddis.2014.307 · 5.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Amyloid refers to insoluble protein aggregates that are responsible for amyloid diseases but are also implicated in important physiological functions (functional amyloids). The widespread presence of protein aggregates but also, in most of the cases, their deleterious effects explain worldwide efforts made to understand their formation, structure and biological functions. We emphasized the role of FTIR and especially ATR-FTIR techniques in amyloid protein and/or peptide studies. The multiple advantages provided by ATR-FTIR allow an almost continuous structural view of protein/peptide conversion during the aggregation process. Moreover, it is now well-established that infrared can differentiate oligomers from fibrils simply on their spectral features. ATR-FTIR is certainly the fastest and easiest method to obtain this information. ATR-FTIR occupies a key position in the analysis and comprehension of the complex aggregation mechanism(s) at the oligomer and/or fibril level. These mechanism(s) seem to present strong similarities between different amyloid proteins and might therefore be extremely important to understand for both disease-associated and functional amyloid proteins. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.
    Biochimica et Biophysica Acta 06/2013; 1828(10). DOI:10.1016/j.bbamem.2013.04.012 · 4.66 Impact Factor